The present invention relates to a suction type sheet feeding device, and more particularly, to a type thereof particularly available for an image recording apparatus.
In a conventional image recording apparatus, a stack of image recording sheets such as developer sheets are accommodated in a sheet cassette, and an uppermost sheet is separated from the remaining sheet stack and fed to a predetermined position such as a sheet path by the sheet feeding mechanism. Conventionally, a roller is used for feeding an uppermost sheet of the sheet stack to the sheet path. The roller pressingly urges the uppermost sheet, so that the sheet surface may be damaged by the roller. Therefore, a suction type sheet feeding device has been proposed. In the suction type sheet feeding device, the uppermost sheet is attracted to a suction cup by bringing the suction cup into intimate contact with the uppermost sheet and applying a negative pressure within the suction cup. Because of the negative pressure, the uppermost sheet is lifted upon lifting motion of the suction foot, and is fed to a proper location such as a pressure developing unit through the sheet feed path.
In such conventional suction type sheet feeding device, a negative pressure generating means including a cylinder and a piston slidably disposed therein is provided, and the negative pressure generating means is in communication with suction cup via a joint member and a hose.
With such conventional arrangement, however, a sealing member such as an O-ring is required so as to provide hermetic construction between a cylinder wall and the piston. Further, relatively large frictional resistance may be provided in the sliding movement of the piston relative to the cylinder wall. In this respect, precise machining to the cylinder wall is required, thereby increasing production costs. Furthermore, in the conventional piston/cylinder arrangement, only one end of the cylinder is connectable to the suction cup for introducing the negative pressure thereto, and therefore, if a plurality of suction cups are intended to be connected to the negative pressure generating means, an intricate joint member is required. Thus, the resultant device becomes increasing costly.
In another aspect, since the suction type sheet feeding means produces the negative pressure, dust and other foreign substances at or around a sheet cassette may be deposits of these materials on the suction cup. Due to the deposition, the sheet attracting performance may be lowered, and mechanical breakdowns may occur. In this standpoint, cleaning to the suction cup has been carried out at every sheet feeding operation. However, the entire sheet feeding period may be prolonged, and therefore, image recording operation requires prolonged time period due to the existence of dead time.